This invention relates in general to video reproduction apparatus such as video cassette recorders. More particularly, this invention relates to video record and/or playback apparatus which is operable in a conventional mode at reduced signal bandwidth, and in a high resolution mode at greater signal bandwidth.
The broadcast color video signal has a broad bandwidth which is utilized only in more expensive consumer video equipment such as television receivers and video cassette recorders. Thus, the composite NTSC color television signal includes a luminance component which is broadcast at a bandwidth of approximately 4.2 MHz and I and Q chrominance components which are broadcast respectively at bandwidths of approximately 1.3 MHz and 0.5 MHz. In the consumer video market, these bandwidths have been limited to reduce equipment cost and to effect simplicity of the processing circuitry. Thus, the luminance component of the color video signal is frequently limited in bandwidth to approximately 3 MHz so that the chrominance components which are carried on a 3.58 MHz subcarrier do not interfere with the luminance component. Similarly, the I chrominance component is frequently limited in bandwidth to the bandwidth of the Q chrominance component in order to simplify the processing circuitry for the chrominance signals. This reduction in bandwidth of the luminance and chrominance components of the color video signal results in a reduction in image resolution and quality.
A reduction in the bandwidths of the color video signal components has been especially evident in consumer video cassette recorders (VCRs). Thus, although studio quality video tape recorders are capable of recording the composite video signal at full bandwidths, such equipment is bulky, expensive, and complex. Broadcast studio recorders generally use one or two-inch wide video tape which requires a bulky and heavy tape transport mechanism which is unsuitable for home video use. Thus, with the advent of relatively inexpensive VCRs for home use, the width of magnetic tape has been reduced to one-half inch (12.5 mm) in the Beta and VHS formats, and to one-third inch (8 mm) in the newer 8 mm format. Moreover, the bandwidths of the luminance component of the composite color signal is limited to approximately 2.5 MHz and of the chrominance component to 0.5 MHz in order to reduce size, cost and complexity of the VCR. Although consumer video cassette recorders generally are capable of recording video at several tape speeds, the bandwidths and consequently the resolution of the recorded signals at the different speeds is not significantly changed. Moreover, the format of the recorded video signal is the same at all speeds. In general, where the tape transport and camera have been combined into a single hand-held unit, only one tape speed (the fastest speed) has been made available to the operator.
Although it has been proposed to increase the speed of the recording head by two or three times the normal speed in order to increase video playback quality, such as in U.S. Pat. No. 4,183,067, issued Jan. 8, 1980 for HELICAL SCAN VTR WITH MEANS FOR DISPLACING HEAD TRACK DIRECTION, inventor N. Kihara et al, the system disclosed in this patent is relatively complex and not compatible with conventional consumer magnetic heads and signal processing circuitry. Thus, as disclosed in this patent two video heads are provided which are offset axially and which lay down video information in tracks which extend only one-half the width of the video tape. This is in contrast to the standard consumer VCR which records a field in a single track which extends the entire width of the tape. In the disclosed patent, the field is recorded in two oblique tracks by different vertically offset heads which extend partially across the width of the magnetic tape. As noted, this recording system is incompatible with a conventional consumer VCR and tapes made with such a recorder could not be interchanged with standard cassette tapes. This patent also discloses at Column 2 thereof the use of a recording head the speed of which may be doubled or tripled to expand the frequency range of the recorded signal without increasing the tape guide drum diameter. As disclosed, two or more successive oblique tracks are used for recording each field of the video signal. These tracks extend substantially across the entire width of the tape so that each track records a segment of the field. As noted in this patent, such a system can cause a significant change in the distance between the head switching point with a resulting "jumping jitter" due to skew distortion.
It has also been proposed to use a time division multiplex scheme to record video signals in the 8 mm mode at increased bandwidths using a conventional magnetic head at normal rotational speed. In this "Timplex System" proposed by the BOSCH Company in 1983 to the 8 mm Video Working Group, the color difference chrominance signals R-Y and B-Y are time compressed and recorded in alternate lines along with a time compressed luminance signal in each line. Thus, although the bandwidth of the video signal is increased, vertical color resolution is reduced by one-half since only one color component signal is recorded for each line. Moreover, there is no disclosure of a bi-modal VCR capable of compatibility with a lower resolution conventional format VCR.
Other time division multiplex systems have been proposed but none of them has given the consumer VCR operator the choice of recording in a conventional relatively lower resolution mode or in a higher resolution, higher image quality mode.